I'm unfamiliar with the term "headstem"; do you mean the headset, the stem, or the entire assembly?
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Neil FeinJun 6 '11 at 4:32

1

@Neil thanks for the comment. I did some research and figured out that I meant the stem. I've updated the question accordingly
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MacJun 6 '11 at 5:00

When you say you've had to replace all those parts this year, how long ago did you buy the bike?
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KibbeeJun 7 '11 at 1:06

I bought it last April. The chain, cog, freewheel and chainring all went in the first 5 months. The seat lasted about a year. The spokes broke from week 2 onwards.
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MacJun 7 '11 at 3:30

I can't decide which is the 'right' answer to this question. Moz has a good analysis that it's impractical to test whether it's failing and a good note that the frame and fork should be solid. Daniel points out that almost all of my replacements have been in 'consumables' anyway and agrees with moz that frame/fork failures are rare.
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MacJun 8 '11 at 3:19

2 Answers
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You are well past the point where I would have told you to throw the bike away and buy a decent one. But IME the frame and fork are usually better built than the components on a bottom-of-the-range bike. There's no real corners to cut on a frame and fork, where they can shave component quality endlessly. Well, they can switch to mild steel tubing but that's rare above the $199 price point. You may well find that the only difference between your bike frame and one on a bike twice the price is the paint.

There's no non-destructive way to tell whether the frame and fork will fail that doesn't cost (a lot) more than the bike is worth. Especially since in this case the bike is worth less than the sum of its parts(1). You could try pulling on the frame/fork to see how flexible it is, but that tells you nothing about how likely it is to fail suddenly (unless it fails while you're testing it). Or you could xray it and have a competant metallurgist examine the images for defects (a single rock climbing carabiner can be thus inspected for perhaps $US200, but a bike is a lot more complex).

If you like the feel of the bike try looking for something similar, probably from the same manufacturer. But looking at their site, you have the mid-range model. I suggest test riding better bikes until you find one you like the feel of. Or do what you have done - replace everything on the bike with better components and hope for the best.

(1) you have replaced most of the components with ones bought retail. So you've paid more markup (and probably labour charges too) than if you had bought a bike with those components already on it. You're probably also suffering from the sunk cost fallacy - you've spent all this money and are reluctant to throw it away. I can't make that call for you, but look at what's left of the original bike and work out how much it will cost to replace it all - especially the wheels. It might be cheaper to buy a better bike and strip the current one for spares.

wow, thanks for the awesome answer. I agonised over whether to upgrade parts or buy a whole new bike when I was replacing the wheels. I don't think I was caught up by the sunk cost fallacy. My analysis was that new wheels was about $200 and then I'd have good components everywhere, except for potentially frame, fork, stem and bars. The alternative I was looking at more than $1000 for a bike with the components I wanted (and even then I couldn't find anything off the shelf with the right mix of components so I'd still be making some changes). So I made the choice to stick with the bike
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MacJun 6 '11 at 7:06

and upgrade parts. The only place I still feel a risk is the forks, stem and bars.
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MacJun 6 '11 at 7:07

sorry I did add that after the question was posted. I've edited it with a comment.
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MacJun 6 '11 at 22:25

Awarded the answer for the comment "But IME the frame and fork are usually better built than the components on a bottom-of-the-range bike. There's no real corners to cut on a frame and fork, where they can shave component quality endlessly. "
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MacJul 7 '11 at 0:28

Basically, nothing you've replaced so far is out of the ordinary for a well-used bike, other than perhaps the seat. I've worn out two front rings, two clusters, easily six chains (which I now replace every thousand miles, just on general principle), and at least a dozen spokes (not counting those I've replaced when I relaced "tired" wheels). Replaced entire wheel sets a couple of times. Also, two bottom brackets, three sets of pedals, and a couple of wheel bearings. Never replaced a freewheel, but they do fail on "good" bikes. This would be in maybe 10,000 miles of riding on three bikes. Someone heavier and/or more muscular (I had polio as a child) would likely wear things out about twice as fast as I do, and off-roading in a bike not designed for it will obviously take an early toll on the bike (as will riding a bike clearly meant for a smaller, lighter person).

I have heard of forks failing (rarely), and, unfortunately, there's no reliable way to know if one is about to fail. Some forks are very well built, others not so well, some are built such that cracks will be obvious, others have designs that will conceal cracks. But looking at the picture of your bike it looks like a reasonably good fork design that would not conceal cracks and not be prone to premature failure.

I've never heard of a catastrophic handlebar or stem failure, and I would judge them quite unlikely.

But there does come a time when it's best to retire an old bike and get a new (and hopefully better) one. I wouldn't discourage you from doing this, but it doesn't seem imperative in your case.

Thanks Daniel. I agree that most of the components I've replaced are 'consumables'. However they have all worn out or broken a lot quicker than the parts I've replaced them with. So I know the bike has been built with sub standard components. I therefore wonder if the forks etc are also substandard.
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MacJun 6 '11 at 7:40

Any bike built for the US market (and not by a fly-by-night company) is going to be built with an eye towards legal liability. You get those stupid safety clips on the front wheel axles because people are too stupid to tighten their quick releases, have the wheels fall off while they're hot-dogging, and then they sue, eg.
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Daniel R HicksJun 6 '11 at 11:15

Good comment, I would hope that these load bearing components will be build solidly. As an aside, I have never understood people's animosity towards the safety tags on the front wheel. Losing the front wheel is my biggest nightmare and anything that might prevent it is more than welcome. There's a (tiny) inconvenience when removing and replacing the wheel but that seems negligable. What is your objection to them?
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MacJun 6 '11 at 22:23

I don't strenuously object to them, I've just never seen the need on a road bike -- you've got to be hot-dogging for your front wheel to come off, even if the QR is loose (which it shouldn't be). Maybe an off-road bike might need them.
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Daniel R HicksJun 7 '11 at 1:37